Though nitrides are inferior to oxides in facilitation of production, not a few of them are known to have characteristics which oxides or other inorganic compounds do not have. Actually, such binary system nitrides as Si3N4, BN, AlN, GaN and TiN are used for various purposes such as substrate material, semiconductor, light emitting diode (hereinafter abbreviated as “LED” as appropriate), structural ceramics and coating agent, and in industrial-scale production.
In addition, large numbers of new substances of ternary or higher nitrides are in production in these years. Among them, phosphor materials with superior characteristics made of particularly oxynitrides or multinary nitrides based on silicon nitride have been developed recently. It is known that these phosphor materials emit yellow to red light when excited by a blue LED or a near-ultraviolet LED.
Such combinations of those phosphors and a blue or near-ultraviolet LED can constitute a light emitting device emitting white light.
For example, Patent Document 1 discloses a white light emitting device in which a blue LED or LD chip of nitride-based semiconductor is combined with a cerium-activated yttrium aluminium garnet phosphor of which Y is partly substituted with Lu, Sc, Gd, or La. The white light emitting device can produce a white light by combining a blue light, generated from the LED, and a yellow light, generated from the phosphor. The white light emitting device is already in practical use for display or the like.
A phosphor comprising a Ce-activated nitride or oxynitride with a JEM-phase silicon oxynitride as the host material is known (Non-Patent Document 1).
In addition, as another phosphor having a nitride as the host material, La3Si6N11:Ce is known (Patent Document 2).
Moreover, as known nitrides containing an alkaline-earth metal element, a trivalent rare-earth element and silicon, SrYbSi4N7 and BaYbSi4N7 are known to have a space group of P63mc (Non-Patent Document 2), and BaEu(Ba0.5Eu0.5)YbSi6N11 is known to have a space group of P213 (Non-Patent Document 3).    [Patent Document 1] Japanese Patent Laid-Open Publication No. Hei 10-190066    [Patent Document 2] Japanese Patent Laid-Open Publication No. 2003-206481    [Non-Patent Document 1] Preprints of Meeting, 316th, Phosphor Research Society, pp. 23    [Non-Patent Document 2] Zeitschrift fur Anorganische undAllgemeine Chemie, 1997, vol. 623, pp. 212    [Non-Patent Document 3] H. Huppertz, a thesis for a doctorate, Bayreuth Univ., 1997